I have always used the red carpet as a 1K, except for two cases: 1) I arrive at the last-minute, there's nobody in line, the red carpet lane is blocked by the tape, and the general boarding lane is open with the GA beckoning me through. I'll take the open lane. Duh. 2) I arrive last-minute for an international flight with two boarding lines going simultaneously, and the line for general boarding is shorter than the red carpet line. Other than that I have always used the red carpet lane and I expect I always will.
I have never scolded someone for being in the red carpet line when I thought they shouldn't. In my experience the GAs are good enough about taking care of that when they scan BPs. The much more frequent problem I see is the area in front of the red carpet being crowded by vultures waiting to swoop into the general boarding line. I peek at people's BPs to know whom I will need to push past when red carpet boarding is called. I always push with a "pardon me" and "excuse me", of course.